Electrical Conductivity Of The Crustal And Mantle Minerals Under High Pressure And High Temperature

Deep Earth detecting is one of the essential part of Geosciences.However,traditional geological method is hard to determine properties of the deep Earth material because the number of natural deep Earth material sample is limited.Geophysics is the most efficient method to detecting the deep Earth.Exploration of the Earth's deep interior is mainly carry out by seismology.Recent development of electromagnetic give us an opportunity to understand other properties of the Earth's deep interior.Comparing with other Geophysics parameters,Electrical conductivity is sensible to the fluid,melt as well as the chemical composition fluctuation of materials.Thus,laboratory conductivity measurements can potentially restrain the physical and chemical environment of the deep Earth interior.In the crustal and mantle minerals,phengite,olivine,garnet,orthorpyroxene and clinopyroxene play important roles in their stable area.Phengite is a critical carrier of water and potassium in sediment as well as in the basaltic layers of subducted slabs.In the sediment layer of subduction slab,the concentration of phengite can be as high as 40 vol%.In addition,phengite can potentially carry water and potassium to the deep Earth until 300 km depth.The Earth's upper mantle is mainly consist of olivine,garnet,orthorpyroxene and clinopyroxene and thus electrical properties of the Earth's upper mantle are determined by such minerals.This study measured the electrical conductivities of phengite before and after dehydration,as well as measured the pressure effect on the electrical conductivity of upper mantle minerals:(1)The pressure generation against applied load for the 14-8 experimental assemblagewas examined,as well as the data validity of this new electrical conductivitymeasurement system;(2)This study investigated the electrical conductivity of olivine,garnet,orthorpyroxeneand clinopyroxene at pressure up to 12 GPa and temperature up to 1500 K,as well asthe electrical conductivity of phengite before and after dehydration at pressure up to12 GPa and temperature up to 1200 K;(3)The results confirm negative pressure effects on the electrical conductivity of olivine,orthorpyroxene and clinopyroxene and positive pressure effects on the electricalconductivity of garnet;(4)Based on the laboratory electrical conductivity data,the electrical conductivity-depth1-D profile of the upper mantle was constructed.The comparison between calculatedprofile geophysical observations indicate that 1)the upper mantle beneath Europe atdepth of 180–350 km might be dry;2)the relative high conductivity value beneathNorth China might be related to wet upper mantle minerals;(5)Dehydration of phengite increased bulk conductivity for more than 10000 times;(6)The conductivity of bulk rock with less than 3 vol% K-rich fluids are in closeagreement with geophysical observations at depths of between 250 km and 300 kmin backarcs beneath the North Philippine Sea and central Argentina.In addition,dehydration products,including K-rich fluids,migrate through the overlying mantlewedge and may cause K-metasomatism.